The present invention relates to the field of targeted delivery of drugs and more specifically involves a multifunctional targeted drug delivery vehicle.
Currently several different molecular scaffolds are used in the synthesis of drug vehicles; notable examples are N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer (20-30 kDa) [42] and other derivatives of polyacrylic acid. However, these are not considered to be biodegradable [43, and references therein], because of their carbon-carbon backbone, and they are problematic due to inevitable contamination by hazardous acrylic acid [44]. Other, degradable scaffolds (e.g. poly(L-glutamic acid) [45] may have unfavorable properties, like rotational restriction around the peptide bond or limited solubility in organic solvents desirable for chemical synthesis and product purification, and, in addition, is supportive of immunogenicity in the structural proximity to other potentially immunogenic structures due to the high hydrogen bond forming capacity of the peptide backbone [45, 46, 47].
Antisense Technology. Antisense oligonucleotides (oligos) that bind and inactivate specific RNA sequences may be one of the best tools for studying gene function, regulation of gene expression, interactions between gene products, and validation of new therapeutic targets for drug development. Antisense oligos offer the promise of safe and effective therapeutics for viral diseases, cancers, and other devastating diseases. Specific antisense oligos that mimic DNA template for RNA production are used to bind to complementary RNA and to prevent protein translation (e.g., of tumor markers) [1].
There are promising data on the use of antisense technology in gliomas. Glioma growth in vitro and in nude mice can be inhibited by antisense to telomerase [2]. A pilot study showed that antisense to IGF-I receptor induced glioma cell apoptosis and resulted in clinical improvements of patients [3]. Several clinical trials are currently using antisense oligos for treatment of other cancers [4]. These studies take advantage of new generation antisense oligos free from insufficient specificity, stability, and non-antisense effects [5]. The most promising varieties of improved oligos are Morpholinos oligos and peptide nucleic acid (PNA) oligos. These varieties have the highest sequence specificity of all antisense types, and maintain this specificity over a very broad concentration range [6, 7, 8, 9, 10 and 11]. A new, rapidly evolving, variant of antisense approach is represented by small interfering RNAs (siRNAs) that are also highly potent gene expression silencers and potential anticancer drugs.
Combined blocking of several molecular markers in vitro and in vivo to prevent tumor progression. This approach has long been used successfully in cancer chemotherapy but has not yet been applied to targeting specific tumor markers. Only following the development of gene/protein array approaches, did it became possible to obtain and correlate data on concerted changes of specific genes during tumor progression and recurrence. Such concerted changes offer a possibility of counteracting simultaneous alterations of several genes in the hope of efficiently blocking tumor development and progression. There are several candidate genes for blocking to stop glioma growth and spread including tyrosine kinase receptors (e.g., EGFR), some growth factors, and antiapoptotic genes that can be potentially used in combination with chemotherapeutic agents to more efficiently prevent tumor growth [12, 13, 14, 15, and 16]. Our earlier studies identified another potential candidate protein, laminin-8, which is overexpressed in brain and breast tumors, correlates with poor prognosis of gliomas and is involved in glioma invasion.
Drug delivery. For direct targeting of cancer cells to treat tumors, the drugs, e.g., monoclonal antibodies, antisense oligos or small molecules (such as Tarceva (erlotinib)), should be able to penetrate the cell membrane. There are three basic methods for intracellular drug delivery, passive diffusion through aqueous channels or pores in the membrane, passive diffusion of lipid-soluble drugs through dissolution in the lipids of the membrane, and carrier-mediated active transport (viral vectors, liposome-mediated gene transfer system, special chemicals) [16, 17]. Brain tissue is especially difficult to treat with drugs because it has a special blood brain barrier with tight junctions between brain microvascular endothelial cells that prevent penetration of water-soluble and ionized or polar drugs [18, 19].
High molecular weight molecules have recently received special attention because of the enhanced permeability and retention (EPR) effect observed in cancer tissue for macromolecules and lipids (MW>45 kDa) [20, 21, and 22]. Unlike small molecule anticancer drugs used today, which do not discriminate tumor from normal tissue, macromolecular (or polymeric) drugs can target tumors with high selectivity through the EPR effect [22, 23]. One such promising drug carriers, poly-L-malic acid (PMLA), has been developed by one of the present inventors [24, 25].